1. Field of the Invention
The invention pertains to a self-pumping, hydropneumatic suspension strut with internal level control, especially for motor vehicles, having an outer tube having a first filling opening and a second filling opening, and an intermediate wall received in the outer tube, the intermediate wall separating a high pressure chamber from a low pressure chamber. The chambers each contain a damping medium, the first filling opening communicating with the low pressure chamber when the intermediate wall is not fully received in the outer tube and being closed by the intermediate wall when the intermediate wall is fully received in the outer tube. A working cylinder is located concentrically inside the outer tube in the high pressure chamber, and a gas filled separating envelope is located between the working cylinder and the outer tube for pressurizing the damping medium in the high pressure chamber. An axially displaceable piston divides the working cylinder into a first working space and a second working space, the first working space being connected to the high pressure chamber. A hollow piston rod supports the axially displaceable piston, the hollow piston rod passing through the second working space and transporting damping medium from the low pressure chamber to the first working space. A pump rod fixed to the intermediate wall and received in the hollow piston rod forms a pump cylinder, the pump rod having a suction tube extending into the low pressure chamber for transporting damping fluid from the low pressure chamber to the piston rod. A piston rod guide is fitted in the outer tube and receives the piston rod therethrough, the piston rod guide having a flow connection connected to the separating envelope. The flow connection communicates with the second filling opening when the piston rod guide is not fully received in the outer tube, and is closed by the outer tube when the piston rod guide is fully received in the outer tube.
2. Description of the Related Art
Suspension struts of the type in which an intermediate wall separates the high-pressure chamber for the low-pressure chamber, and in which a pump rod is attached to this intermediate wall, are already known (e.g., U.S. Pat. No. 6,648,309). This suspension strut can be installed in either of two different positions in a motor vehicle. That is, the piston rod can be inserted so that it extends either upward (FIG. 2) or downward (FIG. 1). In most cases, however, suspension struts of this type are installed on the chassis with the piston rod extending downward, whereas the housing is attached to the vehicle body. This is done to minimize the unsprung masses. It is quite problematic to manufacture this type of design, however, because it must be done horizontally (FIGS. 3 and 4 of U.S. Pat. No. 6,648,309). When the unit is to be filled with gas, the damping medium of the high-pressure chamber must be free to interchange with the damping medium of the low-pressure chamber via the open discharge bore so that the pressure can be equalized; during this process, the compressed gas may not pass from the low-pressure chamber into the pump space, for otherwise the pump itself will not be able to operate properly. In addition, the assembly of a suspension strut of the horizontal type entails a considerable amount of work both to fill the unit with gas and to install the internal parts in the outer tube. An assembly line for the production of suspension struts of the horizontal type therefore occupies a large amount of space.
Conventional suspension struts of a different design are assembled vertically (DE 44 12 842 A1). These suspension struts can be assembled easily, and the assembly equipment can be kept simple.